Caltech Researchers Develop On-Chip Nanoscale Optical Quantum Memory

A computer chip with nanoscale optical quantum memory has been developed that is analogous to a traditional memory chip in a computer.

Artist's representation of the quantum memory device. Courtesy of Ella Maru Studio.
An international team led by engineers at Caltech took advantage of the peculiar features of quantum mechanics, such as superposition in which a quantum element can exist in two distinct states simultaneously, in designing their chip that stores data efficiently and securely.

"Such a device is an essential component for the future development of optical quantum networks that could be used to transmit quantum information," says Andrei Faraon, assistant professor of applied physics and materials science in the Division of Engineering and Applied Science at Caltech.

The technology enables better control of photon/atom interactions and extreme miniaturization of quantum memory devices.

The use of individual photons to store and transmit data has been a goal of engineers and physicists because of their potential to carry information reliably and securely. Because photons lack charge and mass, they can be transmitted across a fiber optic network with minimal interactions with other particles.

Quantum memory stores information via the quantum properties of individual elementary particles. A fundamental characteristic of those quantum properties — which include polarization and orbital angular momentum — is that they can exist in multiple states at the same time. This means that a quantum bit, or qubit, can represent a 1 and a 0 at the same time.

To store photons, Faraon's team created memory modules using optical cavities made from crystals doped with rare-earth ions. Each memory module measured just 700 nanometers wide by 15 microns long. Each module was cooled to about 0.5 Kelvin, and then a heavily filtered laser pumped single photons into the modules. Each photon was absorbed efficiently by the rare-earth ions with the help of the cavity.

The photons were released 75 nanoseconds later, and checked to see whether they had faithfully retained the information recorded on them. “Ninety-seven percent of the time, they had,” said Faraon.

The Caltech team plans to extend the time that the memory can store information, and improve its efficiency. The team also plans to work on ways to integrate the quantum memory into more complex circuits, taking a step towards deploying this technology in quantum networks.